340 On the Influence of Temperaiure of Liqidd Air on Bacteria. 



- 192° C). Further experiments have since been made in which the 

 organisms were again exposed to the temperature of liquid air for a 

 much longer period, viz., seven days. 



The organisms employed were B. typliosus, B. coli coimwinis, B. diph- 

 theria}, B. proteus vulgaris, B. acidi lactici, B. anthmcis (sporing culture), 

 Spirillum cholerm asiaticce, Staphylococcus pyogenes aureus, B. phospho- 

 rescens, a Sarcina, a Saccharomyces, and unsterilised milk. 



Instead of being exposed as formerly on the actual media in which 

 they were growing, the organisms were submitted to the cooling pro- 

 cess in the form of a broth emulsion in hermetically sealed fine quill 

 tubing. This allows of complete immersion, and effects a considerable 

 economy in the amount of liquid air used, besides greatly facilitating 

 manipulation. The liquid air was kindly furnished by Professor 

 Dewar, and the experiment was conducted in his laboratory. 



In the course of the experiment, the loss by evaporation of the 

 liquid air was made up by adding fresh portions from time to time. 

 In this way the temperature of about - 190° C. was maintained unin- 

 terruptedly through the whole period of the experiment. At the same 

 time considerable care had to be taken in conducting the first cooling, 

 in order to avoid fracture of the quill tubes. A preliminary cooling- 

 was therefore effected by means of solid CO2. After the expiration of 

 a week, the tubes were removed with cork-tipped forceps, and placed 

 in a strong glass vessel till thawing was complete. The tubes were 

 then opened, and the contents transferred to suitable culture media. 

 In each case, a direct microscopical examination was made to detect 

 any possible structural changes. 



It is a remarkable fact that, notwithstanding the enormous mechani- 

 cal strain to which the organisms must have been exposed, a strain far 

 exceeding in amount any capable of being produced hitherto by direct 

 mechanical means, not the slightest structural alteration could be 

 detected. 



The sub-cultures made at the conclusion of the experiment grew 

 well, and in no instance could any impairment in the vitality of the 

 organisms be detected. In one or two instances only, growth was 

 slightly delayed, an effect which might have been due to other causes. 

 The photogenic bacteria grew and emitted light, and the samples of 

 milk became curdled. 



The above experiments show that bacteria can be cooled down to 



- 190° C. for a period of seven days without any appreciable impair- 

 ment of their vitality. 



It has not yet been possible to undertake the experiments with 

 liquid hydrogen. 



